Linearteam WinISD Pro
The debate over which design (Sealed vs. Vented vs. Passive radiator vs. Bandpass) is best will, like abortion, likely never end. Suffice it to say that no ONE design is best. They each have their Pro's and Con's. Anyone who tries to convince you otherwise is, at best, a well intentioned fool.
The keyword when considering which type of enclosure to use is...Trade-Off. There are trade-offs between box types, as well as trade-offs within box types.
Let's first begin with the Sealed box. This type of box is completely air tight, and uses the air trapped inside of the box as a suspension (like squeezing an empty plastic Coke bottle with the cap on) for the woofer. The "stiffness" of the suspension is determined by the size of the box in relation to the design of the woofer. A larger suspension (bigger box) will allow the woofer to move more freely, thereby yielding a lower bass response, but at a price in power handling, of course. Likewise, a smaller box will raise the low bass cutoff frequency, but will be able to withstand more power. There is a practical limit as to the upper and lower extremes here as well. You can achieve extremely low cutoff frequencies with sealed boxes, if you use so called Linkwitz-Transform equalizer.
Increasing the box size decreases the Qtc of the box. Lowering the box size raises the Qtc of the box. The suggested range of the Qtc is between 0.5 and 2.0 (the Qtc rating is listed in the Project Window under the Box tab). Overall, here's the scoop on the Sealed box:
Now, let's move on to the vented, or bass-reflex design. This design incorporates one or more tubes or "ports" which allow air to travel in and out of the box as the speaker cone moves in and out. The number of and size of the ports determines the -3dB point of the box. Frequencies which fall below the -3dB point aren't reproduced very well by the box. Here's the scoop on the vented box:
Passive radiator box is a variation of ported box. There, the mass is mounted in very compliant surround. Advantages and disadvantages over ported box are as follows:
And finally, the bandpass box. This design must always be accompanied by a second set of speakers which will play the "mid-bass" frequencies. This is clearly the most difficult box to design and build, and is not intended for beginners. The bandpass box is designed to pass only a small range of bass frequencies. This design allows the user to select very specific woofers to meet very specific needs. Each box/woofer design covers its own part of the spectrum which allows for a more even sound output across the entire spectrum as a whole.
The only real minuses to the bandpass design is that it is a monumental undertaking to properly design and setup a complete system successfully. I recommend you experiment with the sealed and/or vented designs first, and then go out and buy a book which deals with bandpass design/construction prior to building your first bandpass system. With your book in hand, use WinISD to do all the "what-if" scenarios for you. WinISD will go as deep as you want it to!